The present invention relates to a sheet-feeding device and imaging system incorporating such device. More particularly, the invention relates to an apparatus and method for measuring paper storage in an image forming apparatus.
A quality imaging system such as a printer or a photocopier requires consistent and error-free feeding of paper from a supply tray. One type of paper supply tray includes a ramped surface or dam at an end that is adjacent to the paper path in the printer. A roller assembly includes a roller that engages the top sheet of a paper stack held in the supply tray. The roller moves the top sheet up the dam and into the paper path of the printer.
Many photocopiers and printers include at least one feature that allows a user to easily determine when a paper supply tray is depleted of paper. However in instances, a user may desire to have advance notice of an empty feed paper tray. For example, if a paper supply tray has a capacity of 200 sheets, it may be desirable for a user to be aware that the supply tray is approximately half full, or contains approximately 100 sheets. Or, it may be desirable for a user to know that the supply tray is nearly empty so that paper can be replenished to complete a print job without interruption. Further, it may be desirable for a user to know that a number of printed pages in a requested print job is larger than an approximate number of sheets in the supply tray so that paper can be added prior to commencing a print job.
Various methods and apparatus exist for determining the approximate paper level within a paper supply tray. Such paper level indicators require relatively expensive additional printer hardware to sense the paper level; thereby increasing the cost of the printer. Generally, these methods and apparatus are used in conjunction with a supply tray wherein the paper rests directly on the bottom of the supply tray. For example, one method uses an arm that rests on the top of the paper stack and uses hardware to detect the angle of the arm.
In another paper level indicator, a stack of paper is disposed within a feeder module such that the trailing edges of the paper sheets are disposed at an acute angle relative to a bottom surface of the feeder module. A light source is disposed on top of the feeder module and a sensor is disposed on the bottom of the feeder module. As the sheets in the paper stack are used, the sensor receives more of the light that is output by the light source. The sensor operates a suitable electrical circuit to provide a xe2x80x9clowxe2x80x9d warning to a user when the height of the stack is such that the sensor is substantially exposed. This indicator is expensive and sometimes inaccurate.
There is a need for simple and error-free apparatus and method for detecting a paper level in a supply tray, particularly there is a need for a paper sensor system that can be used in conjunction with a novel imaging system that includes a drive assembly including a pick roller for moving a top sheet of a supply of sheets in a paper tray to a ramp, wherein the drive assembly is configured to maintain a constant spaced relationship between the roller and the ramp when the roller is moving a top paper sheet to the ramp.
The present invention meets these needs by providing an imaging system comprising an imaging subsystem for forming an image on a sheet, a tray for holding a supply of sheets, a ramp for directing a sheet from the tray into a paper path, a sensor in the vicinity of the paper path, a drive assembly and a processor connected to the drive assembly and the sensor. The drive assembly includes a movable roller configured to move the sheet into the paper path by moving a top sheet of a supply of sheets in the tray to the ramp. The sensor is configured to detect a sheet traveling in the paper path from the tray and to provide an output signal in response to the detection. The processor is configured to control movement of the roller, to receive and store an initial sheet level value, to receive the output signal from the sensor and to calculate a time, t, from activating the drive assembly to receiving the sensor output signal and to accordingly adjust the initial sheet level value.
In an embodiment, an imaging system comprises an imaging subsystem for forming an image on a sheet, a tray for holding a supply of sheets, a ramp for directing a sheet from the tray into a paper path, a sensor in the vicinity of the paper path, a drive assembly and a processor connected to the sensor. The drive assembly includes a roller for moving a top sheet of the supply of sheets in the tray to the ramp with a reciprocating roller stroke; the drive assembly being configured to maintain a constant roller stroke distance between the roller and the ramp. The sensor is configured to detect a sheet traveling in the paper path from the tray and to provide an output signal in response thereto. The processor is configured to receive the sensor output signal and to accordingly adjust a value representing a sheet level in the tray.
In another embodiment, a method for measuring sheet levels in an imaging system paper tray, comprises recording a start time that a roller engages a paper sheet to feed the sheet from the paper tray to a paper path of the imaging system and sensing a time the sheet passes a location along the paper path. A time difference between the start time and the time sensed is processed to provide a signal that represents a supply of sheets in the paper tray.